Evaluation of estrogen receptor (ER) with 18F-fluoroestradiol in biopsy-proven ER positive breast cancer patients resistant to hormonal therapy

Objectives Some breast cancer patients with biopsy-proven estrogen receptor (ER) fail to respond to or develop new lesions during hormonal therapy, suggesting either transformation to ER-negative state or ineffective current therapeutic due to other mechanisms such as tumor growth factors. We have explored the usefulness of PET imaging with 18F-16alpha-fluoro-17beta-estradiol (FES) for examining ER status of each lesion.

Methods FES-PET was performed on 7 patients (age 39-72) who had biopsy-proven ER-positive primary breast cancer but did not respond to or developed metastatic lesions during hormonal therapy (estrogen antagonist, LH-RH agonist, or aromatase inhibitor). The subjects underwent whole-body PET/CT scan starting 60 minutes post injection of 178-211 MBq of FES.

Results FES uptake was observed in the lesions of 4 cases (primary lesion, bone, lung, and pleural metastasis). In one of them, 2 of 4 vertebral bone metastatic lesions were FES positive, while the others were negative. In another case, accumulation in the FDG-avid liver lesion appeared comparable to the surrounding normal tissue and was not detected visually. FES uptake was not observed in the lesions of the other 2 cases (primary, lymph node). The SUV of FES positive lesions ranged from 1.0 to 8.1.

Conclusions Breast cancer lesions that do not respond to hormonal therapy may have variable ER status. FES-PET is useful as a non-invasive tool for examining ER for each lesion and may provide valuable information for management of such patients.